Electrode array catheter

Abstract: An electrode array catheter, typically used for mapping, pacing and ablation, includes an electrode assembly 2, 62 which may be slidably mounted within a delivery sheath for movement between retracted and deployed positions. The electrode assembly includes an ablation electrode 10, 90 and a plurality of mapping electrodes 26, 114 which are grouped in pairs and naturally assume a three-dimensional array when deployed. The electrodes are distributed to contact a portion of the chamber wall 130 surrounding the target site. The electrode assembly tip has a coiled conical shape 24 in one embodiment and has a number of axially extending, radially outwardly curved arms 118 in another embodiment. A flat flexible circuit 110, having axially extending electrode traces 112 connecting proximal terminals 108 to distal electrode pads 114, is slit 116 axially and is performed and to create the curved arms.

Description: The present invention relates generally to steerable catheters, and more specifically, but not exclusively, to steerable electrophysiology catheters for use in mapping and ablation of the heart. The heart includes a number of pathways which are responsible for the propagation of signals necessary for normal electrical and mechanical function. The present invention is concerned with treatment of tachycardia, abnormally rapid rhythms of the heart caused by the presence of an arrhythmogenic site or accessory pathway which bypasses or short circuits the normal pathways in the heart. Tachycardias may be defined as ventricular tachycardias (VTs) and supraventricular tachycardias (SVTs). VTs originate in the left or right ventricle and are typically caused by arrhythmogenic sites associated with a prior myocardial infarction. SVTs originate in the atria and are typically caused by an accessory pathway. Treatment of both ventricular and supraventricular tachycardias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/ defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, drugs typically only mask the symptoms and do not cure the underlying cause. Implantable devices, on the other hand, usually can correct an arrhythmia only after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem usually by ablating the abnormal arrhythmogenic tissue or accessory pathway responsible for the tachycardia. The catheter-based treatments rely on the application of various destructive energy sources to the target tissue, including direct current electrical energy, radiofrequency electrical energy, laser energy, and the like. Of particular interest to the present invention, are radiofrequency (RF) ablation protocols which have proven to be highly effective in tachycardia treatment while exposing the patient to minimum side effects and risks. Radiofrequency catheter ablation is generally performed after an initial mapping procedure where the locations of the arrhythmogenic sites and accessory pathways are determined. After mapping, a catheter having a suitable electrode is introduced to the appropriate heart chamber and manipulated so that the electrode lies proximate the target tissue. Radiofrequency energy is then applied through the electrode to the cardiac tissue to ablate a region of the tissue which forms part of the arrhythmogenic site or the accessory pathway. By successfully destroying that tissue, the abnormal signaling patterns responsible for the tachycardia cannot be sustained. Methods and systems for performing RF ablation by controlling temperature at the ablation site are described in WO93/20770 entitled "Method and System for Radiofrequency Ablation of Cardiac Tissue ". Catheters designed for mapping and ablation frequently include a number of individual electrode bands mounted to the distal tip of the catheter so as to facilitate mapping of a wider area in less time, or to improve access to target sites for ablation. As described in that application, it is frequently desirable to deflect the distal tip of the catheter into a non-linear configuration such as a semicircle, which facilitates access to substantially all of the heart walls to be mapped or ablated. Such deflection may be accomplished through the use of pull wires secured to the distal tip which can be tensioned from the proximal end of the catheter to deflect the tip in the desired configuration. In addition, mapping and ablation catheters may facilitate rotational positioning of the distal tip, e.g. by rotating the entire catheter from the proximal end, or by exerting torque on a core wire secured to the distal tip without rotating the catheter body itself. Catheters utilized in radiofrequency ablation are inserted into a major vein or artery, usually in the neck or groin area, and guided into the chambers of the heart by appropriate manipulation through the vein or artery. Such catheters must facilitate manipulation of the distal tip so that the distal electrode can be positioned against the tissue region to be ablated. The catheter must have a great deal of flexibility to follow the pathway of the major blood vessels into the heart, and the catheter must permit user manipulation of the tip even when the catheter is in a curved and twisted configuration. Because of the high degree of precision required for proper positioning of the tip electrode, the catheter must allow manipulation with a high degree of sensitivity and controllability. In addition, the distal portion of the catheter must be sufficiently resilient in order to be positioned against the wall of the heart and maintained in a position during ablation without being displaced by the movement of the beating heart. Along with steerability, flexibility, and resiliency, the catheter must have a sufficient degree of torsional stiffness to permit user manipulation from the proximal end. One of the problems with current technology relates to quickly mapping a large surface area of the heart. Finding the target site using conventional catheters with linear electrode orientations is a tedious activity requiring multiple catheter placements. Balloon or basket type mapping catheters, providing three dimensional arrays of endocardial mapping electrodes, have been developed. However, these arrangements are typically designed to engage virtually the entire chamber wall, as opposed to a part or region of the chamber wall. Such full-chamber type mapping catheters lack the ability to direct an ablation electrode to a target site, so they are used for mapping only. Also, by virtue of their design, which is intended to cover virtually the entire chamber wall, these full-chamber type mapping catheters will necessarily lack the ability to concentrate the mapping electrodes at the region of the target site. Thus, while information may be obtainable from the entire chamber wall much of it may not be useful since it is not near the target site. Also, because these devices fill an entire heart chamber, they may partially occlude blood flow or cause coagulation of blood, that is, create blood clots. US 5,181,511 discloses an apparatus for antitachycardia pacing using a virtual electrode. Three or more electrodes are connected to the source of antitachycardia pacing therapy based on the relative distances determined and in such a manner as to create a virtual electrode at the focus site upon delivery of the therapy to the heart. Different electrode assembly configurations are disclosed. WO93/15790 discloses a biplanar deflectable catheter for arrhythmogenic tissue ablation. The distal catheter tip can be moved in any direction in a manner such that the distal tip is capable of accessing any point on the wall of the chamber entered. EP 0 479 435 discloses a multiple electrode deployable lead. The lead distal end defines a plurality of separate, curvilinear electrodes which naturally extend laterally outwardly in a curved arrangement from the remainder of the lead. According to the invention, there is provided a steerable electrode array catheter, for insertion into a heart chamber for placement of multiple electrodes against the heart chamber wall in the vicinity of a target site, comprising: an electrode assembly including a distal end having a plurality of electrodes which naturally assume an array when said distal end is unconstrained, said electrodes being distributed on said distal end so as to be able to contact a limited portion of the chamber wall surrounding the target site; means for steering the distal end of the electrode assembly within the heart chamber to the target site; characterized in that the electrode assembly includes a resilient electrode body which naturally assumes a coiled, conical shape when in the deployed position. Electrode array catheters according to the present invention are useful for a variety of electrophysiology procedures, including mapping, pacing and ablation therapy. The catheter may include a flexible delivery sheath having a hollow interior and proximal and distal ends. The invention addresses and solves the problem of mapping a portion of the chamber wall of the heart in the vicinity of a target site in a relatively short time span. Preferably, an electrode assembly is slidably mounted within the hollow interior of a delivery sheath for movement between retracted and deployed positions. The electrodes naturally assume a three dimensional array when they are at the deployed position. The electrodes are distributed to be able to contact and conform to the position of the chamber wall at the target site when in the deployed position. One or more of the electrodes, which may include a central electrode, are preferably higher power, ablation electrodes. The ablation electrodes may be physically larger than the other electrodes, typically electrodes used for mapping or pacing, to accommodate higher energy flows. The electrode assembly assumes a coiled conical shape when in the deployed position. Electrodes are preferably at spaced apart positions along the coiled, conically shaped electrode body to create a series of electrode pairs. The mapping electrodes are not typically suitable for ablation due to the size limitations of the conductor wires and the size of the electrodes. However, the current carrying capacity of the wires, signal traces and electrode pads could be increased, such as by increasing their size, a change of material, by cooling the various components, etc. Also, techniques may be developed which allow the delivery of energy sufficient to ablate tissue along what is now considered low energy wires, traces and electrodes. With the present invention, ablation may be successful with lower power/smaller lesions since the electrode array can be more accurately located near the target site; this accuracy of placement may permit local "mapping/pacing" electrode pairs to be used for RF energy delivery and ablation. One of the advantages of the invention is that, by producing an array of electrodes designed to engage only a portion of the chamber wall of the heart, a relatively large, but much less than the entire, surface area of the heart can be mapped precisely and in a relatively short time span. Since the physician generally knows the approximate area where the target site is located on the chamber wall surface, mapping of the entire chamber wall is not generally needed. Therefore, a more localized concentration of electrodes can be used with the present invention than would be typical of a chamber-filling device. This helps the device made according to the present invention be simpler to use and the resulting information easier to process. Conventional chamber-filling mapping probes also may not be suitable for ablation, only mapping. The pinpointing of a target site for ablation can be speeded up dramatically without the multiple catheter placements necessary with conventional linear electrodes. The invention also permits the application of a greater number of electrodes against the portion of the chamber wall being investigated than is possible with conventional large diameter linear electrode catheters. Another advantage of the invention over the prior art is the ability of the electrodes to conform to the region of the chamber wall being mapped. Electrodes, which preferably are in closely spaced pairs, provide the user with specific information regarding the electrical activity within the region regardless of the surface contour. Other features and advantages of the invention will appear from the following description, given by way of example only, in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings. Fig. 1 is a simplified perspective view of an electrode assembly of a first embodiment of the invention having a coiled, conical tip; Fig. 2 is an enlarged end view of the coiled, conical tip of Fig. 1; Fig. 2A illustrates an electrode assembly tip having an inverted conical shape; Figs. 3A-3D are cross-sectional views of the electrode assembly taken along lines 3A-3A through 3D-3D in Fig. 1 respectively; Fig. 4 is an enlarged cross-sectional view taken along line 4-4 of Fig. 2; Fig. 5 is a simplified side view of a steerable delivery catheter used with the electrode assembly of Fig. 1 to create a first embodiment of an electrode array catheter made according to the invention; Figs. 6 and 7 are cross-sectional views taken along lines 6-6 and 7-7 of Fig. 5, respectively; The invention is directed to an electrode array catheter such as shown in Figs. 1-7. An exemplary catheter constructed in accordance with the principles of the present invention includes an electrode assembly 2 which will be described with reference to Figs. 1-4 and a steerable delivery catheter 4 shown in Figs. 5-7. All dimensions given for each embodiment are exemplary only, and it will be appreciated that specific dimensions may be varied considerably while remaining within the scop of the present invention. Electrode assembly 2 includes an electrode catheter body 6 extending from an electrical connector 8 at a proximal end to a tip electrode 10 at a distal end. Body 6, as shown in Figs. 3A and 3B, includes a 0.46 mm (.018 inch) diameter stainless steel support mandrel 12 extending from connector 8 to a transition region 13 and a 0.31 mm (.015 inch) core 14 extending from core transition region 13 to tip electrode 10. A 0.71 mm (.028 inch) OD/0.51 mm (.020 inch) ID stainless steel hypotube 16 surrounds support mandrel 12 and an initial portion of core 14. See Figs. 3A-3C. Hypotube 16 extends a relatively short distance past core transition region 13 and is crimped, as shown in Figs. 3B and 3C, onto the abutting ends of support mandrel 12 and core 14 at transition region 13. A number, sixteen in the preferred embodiment, of insulated conductor wires 18 are located about hypotube 16 within an outer Pebax® jacket 20 having a 1.12 mm (.044 inch) ID and a 1.32 mm (.052 inch) OD. Pebax® is the trademark for a polyether block polyamide copolymer made by Elf Atochem, Inc. of Philadelphia, PA. Just past transition region 13, a smaller Pebax® jacket 22 having a 0.79 mm (.031 inch) ID and a 0.94 mm (.037 inch) OD is used. core 14 is preferably made from a super elastic spring material, such as nickel-titanium alloys (NiTi), such as that available from Furukawa Electric Company Ltd. of Tokyo, Japan. NiTi is preferred for core 14 because it is very resilient and has a very good spring memory for its prior shape, even when highly flexed. Other highly deformable spring materials, such as spring steel or braided/coiled spring materials, might also be used. In the embodiment of Figs. 1-4, the tip 24 of the catheter is made so that it assumes a coiled conical shape as shown in Figs. 1 and 2. Electrode assembly 2, when inserted into delivery catheter 4, will have its tip 24 in a straightened orientation since it is, prior to deployment, housed within delivery catheter 4. Only after tip 24 is moved to its deployed position external of delivery catheter 4 will the tip assume its coiled conical shape. Tip 24 can also be made as an inverted coil tip 24a, as illustrated in Figs. 2A. Tip 24 includes fifteen electrodes 26 along its length. Fourteen of electrodes 26 are spaced apart by about 0.5-2.0 mm, typically about 1 mm, to form 7 pairs of electrodes. Distal electrode 27 is paired with tip electrode 10, as shown in more detail in Fig. 4 for mapping. NiTi core 14 is seen to be surrounded by a polyimide sleeve 28 having a 0.45 mm (.0179 inch) OD and a 0.40 mm (.0159 inch) ID. Sleeve 28 provides electrical insulation between core 14 and the electrodes 26/conductor wires 18. Conductor wires 18 are electrically connected to electrodes 26 and tip electrode 10 in the manner indicated in Fig. 4. Tip electrode 10 and the conductor wire 18 connected to the tip electrode are sufficiently heavy duty to permit electrode 10 to be used as an ablation electrode using RF electrical energy. Tip electrode 10 can also be used for mapping in conjunction with electrode 27 positioned adjacent the tip electrode. It may be desired to use electrodes other than tip electrode 10 for ablation. This may be accommodated by increasing the axial length of selected electrodes 26 from about 0.5 mm to 1.0 mm to about 1 to 10 mm. To maintain the desired flexibility of tip 24, the extended length ablation- capable electrodes 26 can be made, for example, as a spiral coil about sleeve 28 instead of a band as illustrated in Fig. 4. Also, ablation-capable electrodes 26 could be made of braided material. Steerable delivery catheter 4, see Figs. 5-7, is designed for use with electrode assembly 2. Catheter 4 has a hollow interior 30 extending along its entire length from Luer lock fitting 32 at its proximal end to a tip ring 34 at its distal end. Catheter 4 includes a catheter body 36 having a Pebax® jacket 38 surrounding a braided layer 40. A TFE liner 42 is within braided layer 40 and provides a lubricous surface for the passage of electrode assembly 2 within hollow interior 30 formed within liner 42. Other lubricious materials, such as FEP, ETFE or PE, could be used instead of TFE for liner 42. Hollow interior 30 is formed eccentrically within TFE liner 42 to provide room for an axial bore 44 housing a TFE-coated manipulator wire 46. Manipulator wire 46 has a ball 48 at its distal end which is too large to fit through a bore 50 in tip ring 34. The proximal end, not shown, of manipulator wire is connected to a tip deflection control 52 mounted to a handle 54. The distal end of catheter body 36 includes a deflecting section 56 distal of a jacket transition line 58. Deflecting section 56 is less stiff than the proximal end of catheter body to allow deflecting section 56 to be sufficiently flexible for the proper guidance by wire 46 while providing appropriate structural integrity for the remainder of catheter body 36. Tip deflection control 52 is preferably an axially movable type so that pulling on control 52 causes the distal end of catheter body 36 to deflect. Other types of controls could be used as well. Also, more than one manipulator wire 46 could be used. In use, electrode assembly 2 has its tip 24 preformed into the coiled, conical shape of Fig. 1. Electrode tip 24 is then inserted through Luer lock fitting 32 and into hollow interior 30. Electrode assembly 2 is continued to be directed through hollow interior 30 until tip electrode 10 is just proximal to deflecting section 56. Using appropriate surgical techniques, the catheter is guided into the heart chamber under consideration. Near the target site to be investigated or treated, electrode assembly 2 is pushed axially and distally until tip 24 extends past tip ring 34 and assumes a coiled, conical shape. Tip 24 can then be placed against the chamber wall at the target site under consideration. If desired, tip 24 may be manipulated to deflect laterally and torque the longitudinal axis of body 6 prior to being placed against the chamber wall. The flexibility and resilience of tip 24 is such that it will closely conform to the shape of the chamber wall at the target site, whether it be flat, convex, concave, or a combination. This conformance ensures a maximum number of electrodes 26 will actually contact the chamber wall. A separate conductor could be used on steerable delivery catheter to deliver RF energy for ablation to an electrode mounted as the tip ring 34. It may be possible to do this through the use of manipulator wire 46 as both the manipulator wire and as an electrical conductor. The present invention is divided from EP-A-0728029.

Claims: A steerable electrode array catheter, for insertion into a heart chamber for placement of multiple electrodes against the heart chamber wall in the vicinity of a target site, comprising: an electrode assembly (2) including a distal end having a plurality of electrodes (24) which naturally assume an array when said distal end is unconstrained, said electrodes being distributed on said distal end so as to be able to contact a limited portion of the chamber wall surrounding the target site; means for steering the distal end of the electrode assembly (2) within the heart chamber to the target site; characterized in that the electrode assembly includes a resilient electrode body which naturally assumes a coiled, conical shape when in the deployed position. The catheter of claim 1 wherein the steering means includes means for directly deflecting the distal end of the electrode assembly. The catheter of any of claims 1 or 2 being a flexible delivery catheter (4) having a catheter body with a hollow interior (30), a proximal end and a distal end, the electrode assembly slidably mounted within the hollow interior of the delivery catheter for movement between a retracted position, at least substantially housed within the hollow interior, and a position, extending from the distal end of the delivery catheter. The catheter of any of claims 1, 2 or 3 wherein the electrode assembly includes an ablation electrode.

Inventors: JARACZEWSKI RICHARD S, LADD KEVIN C, MAGUIRE MARK A, REYES RAMIRO L, JARACZEWSKI, RICHARD S., LADD, KEVIN C., MAGUIRE, MARK A., REYES, RAMIRO L.
Applicants: MEDTRONIC CARDIORHYTHM
Application year: 1994
Main classification: A61N1
IPC codes: A61N1, A61B5, A61B18